The hypothesis that cancer results from an impairment of the process of cell differentiation will be tested in tumors of the hematopoietic system. The number of different sequences (complexity) comprising the cytoplasmic polyadenylated RNA (mRNA) and the relative abundancy of these sequences will be determined. The objectives are to determine if the abundancy patterns differ among normal and malignant tissues. Cytoplasmic polyadenylated RNA, which actually does not include all the mRNA species in a cell, will be isolated, transcribed into cDNA and a cDNA library prepared. Specific cDNA clones will be selected and will be used to probe gene expression. The hybridization properties of the probe will be taken as representative of the intracellular mRNA population.